As demand for even higher performance of tires has increased in recent years, techniques such as blending of silica to a tire to achieve low rolling resistance have come to be known. However, the use of silica may present problems such that the silanol groups present on the surface of the silica particles tend to enhance the aggregation of the silica via formation of hydrogen bonding, thereby increasing the Mooney viscosity of the rubber composition during kneading, and deteriorating processability.
To improve dispersibility of silica, it is advantageous to add a sulfur-containing silane coupling agent with high reactivity. However, such a sulfur-containing silane coupling agent may not be blended in a large amount due to problems in processing, such as scorching of unvulcanized rubber. Thus, there have been problems such as insufficient dispersion of silica leading to failure to achieve good low rolling resistance.
For example, as a conventional technique to enhance processability of a silica-containing rubber composition, Japanese Unexamined Patent Application Publication No. 2006-052407A discloses a technique in which fatty acid and trimethylolpropane are added to a rubber as additives. However, none of conventional technologies has solved the problems described above of the rubber composition yet.